[FRAME] Message Queue use proper overweight limit (#1873)

Changes:
- Use a sensible limit for the overweight-cutoff of a single messages
instead of the full configured `ServiceWeight`.
- Add/Update tests

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

substrate/frame/message-queue/src/tests.rs

@@ -266,6 +266,44 @@ fn service_queues_suspension_works() {
 	});
 }
 
+#[test]
+#[cfg(debug_assertions)]
+#[should_panic(expected = "Not enough weight to service a single message.")]
+fn service_queues_low_weight_defensive() {
+	use MessageOrigin::*;
+	build_and_execute::<Test>(|| {
+		DefaultWeightForCall::set(21.into());
+		// Check that the integrity test would catch this:
+		assert!(MessageQueue::do_integrity_test().is_err());
+
+		MessageQueue::enqueue_message(msg("weight=0"), Here);
+		MessageQueue::service_queues(104.into_weight());
+	});
+}
+
+/// Regression test for <https://github.com/paritytech/polkadot-sdk/pull/1873>.
+#[test]
+fn service_queues_regression_1873() {
+	use MessageOrigin::*;
+	build_and_execute::<Test>(|| {
+		DefaultWeightForCall::set(20.into());
+
+		MessageQueue::enqueue_message(msg("weight=100"), Here);
+		assert_eq!(MessageQueue::service_queues(100.into_weight()), 100.into());
+
+		// Before the MQ this would not emit any events:
+		assert_last_event::<Test>(
+			Event::OverweightEnqueued {
+				id: blake2_256(b"weight=100"),
+				origin: MessageOrigin::Here,
+				message_index: 0,
+				page_index: 0,
+			}
+			.into(),
+		);
+	});
+}
+
 #[test]
 fn reap_page_permanent_overweight_works() {
 	use MessageOrigin::*;
@@ -1150,6 +1188,116 @@ fn permanently_overweight_book_unknits_multiple() {
 	});
 }
 
+#[test]
+fn permanently_overweight_limit_is_valid_basic() {
+	use MessageOrigin::*;
+
+	for w in 50..300 {
+		build_and_execute::<Test>(|| {
+			DefaultWeightForCall::set(Weight::MAX);
+
+			set_weight("bump_service_head", 10.into());
+			set_weight("service_queue_base", 10.into());
+			set_weight("service_page_base_no_completion", 10.into());
+			set_weight("service_page_base_completion", 0.into());
+
+			set_weight("service_page_item", 10.into());
+			set_weight("ready_ring_unknit", 10.into());
+
+			let m = "weight=200".to_string();
+
+			MessageQueue::enqueue_message(msg(&m), Here);
+			MessageQueue::service_queues(w.into());
+
+			let last_event =
+				frame_system::Pallet::<Test>::events().into_iter().last().expect("No event");
+
+			// The weight overhead for a single message is set to 50. The message itself needs 200.
+			// Every weight in range `[50, 249]` should result in a permanently overweight message:
+			if w < 250 {
+				assert_eq!(
+					last_event.event,
+					RuntimeEvent::MessageQueue(Event::OverweightEnqueued {
+						id: blake2_256(m.as_bytes()),
+						origin: Here,
+						message_index: 0,
+						page_index: 0,
+					})
+				);
+			} else {
+				// Otherwise it is processed as normal:
+				assert_eq!(
+					last_event.event,
+					RuntimeEvent::MessageQueue(Event::Processed {
+						origin: Here,
+						weight_used: 200.into(),
+						id: blake2_256(m.as_bytes()),
+						success: true,
+					})
+				);
+			}
+		});
+	}
+}
+
+#[test]
+fn permanently_overweight_limit_is_valid_fuzzy() {
+	use MessageOrigin::*;
+	let mut rng = rand::rngs::StdRng::seed_from_u64(42);
+
+	for _ in 0..10 {
+		// Brainlet code, but works...
+		let (s1, s2) = (rng.gen_range(0..=10), rng.gen_range(0..=10));
+		let (s3, s4) = (rng.gen_range(0..=10), rng.gen_range(0..=10));
+		let s5 = rng.gen_range(0..=10);
+		let o = s1 + s2 + s3 + s4 + s5;
+
+		for w in o..=o + 300 {
+			build_and_execute::<Test>(|| {
+				DefaultWeightForCall::set(Weight::MAX);
+
+				set_weight("bump_service_head", s1.into());
+				set_weight("service_queue_base", s2.into());
+				// Only the larger one of these two is taken:
+				set_weight("service_page_base_no_completion", s3.into());
+				set_weight("service_page_base_completion", 0.into());
+				set_weight("service_page_item", s4.into());
+				set_weight("ready_ring_unknit", s5.into());
+
+				let m = "weight=200".to_string();
+
+				MessageQueue::enqueue_message(msg(&m), Here);
+				MessageQueue::service_queues(w.into());
+
+				let last_event =
+					frame_system::Pallet::<Test>::events().into_iter().last().expect("No event");
+
+				if w < o + 200 {
+					assert_eq!(
+						last_event.event,
+						RuntimeEvent::MessageQueue(Event::OverweightEnqueued {
+							id: blake2_256(m.as_bytes()),
+							origin: Here,
+							message_index: 0,
+							page_index: 0,
+						})
+					);
+				} else {
+					assert_eq!(
+						last_event.event,
+						RuntimeEvent::MessageQueue(Event::Processed {
+							origin: Here,
+							weight_used: 200.into(),
+							id: blake2_256(m.as_bytes()),
+							success: true,
+						})
+					);
+				}
+			});
+		}
+	}
+}
+
 /// We don't want empty books in the ready ring, but if they somehow make their way in there, it
 /// should not panic.
 #[test]
@@ -1447,3 +1595,37 @@ fn service_queue_suspension_ready_ring_works() {
 		);
 	});
 }
+
+#[test]
+fn integrity_test_checks_service_weight() {
+	build_and_execute::<Test>(|| {
+		assert_eq!(<Test as Config>::ServiceWeight::get(), Some(100.into()), "precond");
+		assert!(MessageQueue::do_integrity_test().is_ok(), "precond");
+
+		// Enough for all:
+		DefaultWeightForCall::set(20.into());
+		assert!(MessageQueue::do_integrity_test().is_ok());
+
+		// Not enough for anything:
+		DefaultWeightForCall::set(101.into());
+		assert_eq!(MessageQueue::single_msg_overhead(), 505.into());
+		assert!(MessageQueue::do_integrity_test().is_err());
+
+		// Not enough for a single function:
+		for f in [
+			"bump_service_head",
+			"service_queue_base",
+			"service_page_base_completion",
+			"service_page_base_no_completion",
+			"service_page_item",
+			"ready_ring_unknit",
+		] {
+			WeightForCall::take();
+			DefaultWeightForCall::set(Zero::zero());
+
+			assert!(MessageQueue::do_integrity_test().is_ok());
+			set_weight(f, 101.into());
+			assert!(MessageQueue::do_integrity_test().is_err());
+		}
+	});
+}